The aminopyrimidine CHIR99021 is the most selective inhibitor of glycogen synthase kinase 3i� (GSK-3i�) reported to date1,2. Unlike other potent inhibitors of GSK-3, CHIR99201 does not exhibit cross-reactivity against cyclin-dependent kinases (CDKs) and shows a 350-fold selectivity toward GSK-3i� compared to CDKs3. along with the elimination of differentiation-inducing signaling from mitogen-activated protein kinases, using CHIR99021 to block the activity of GSK-3i� enables the self-renewal of embryonic stem cells4. Stemoleculea, c CHIR99021 in Solution is a ready to use 10 mM stock solution for stem cell culture.